1. Field of the Invention
The present invention relates to an electrode structure of a plasma display panel (PDP), and more particularly, to an electrode structure of a PDP with a small discharge gap.
2. Description of the Prior Art
A plasma display panel (POP) is one kind of flat display using gas discharges to create brilliant images. Advantages of the PDP include thin and lightweight design, large display size, and wide viewing angle. The luminescent principle of the PDP involves the production of ultraviolet (UV) rays by plasma first, followed by irradiation of the UV rays to produce visible light. The production efficiency of plasma greatly influences the luminescent efficiency of the PDP. The luminescent efficiency of the PDP can be improved by many methods. For examples increasing UV production can improve the luminescent efficiency of the PDP, but increasing the luminescent efficiency of the fluorescence material is difficult. Nowadays, change of the filling gas and the electrode structure of the PDP will increase, the UV production.
Please refer to FIG. 1. FIG. 1 is a cross-sectional view of a PDP 10 in the prior art. The PDP 10 includes a front substrate 12 and a back substrate 14 positioned in parallel, a discharge gas (not shown) filled between the front substrate 12 and the back substrate 14, and two sustaining electrodes 16 formed on the surface of the front substrate 12. A discharge gap 17 is defined between the two sustaining electrodes 16. Two auxiliary electrodes 18 are formed above and parallel to the two sustaining electrodes 16 on the front substrate 12. A plurality of address electrodes 20 are formed on the surface of the back substrate 14 and perpendicular to the sustaining electrodes 16.
The PDP 10 further includes a dielectric layer 22, a protective layer 24, a plurality of ribs (not shown), and a fluorescent layer 26. The dielectric layer 22 covers the front substrate 12, and the protective layer 24 formed above the dielectric layer 22. The ribs are formed parallel to each other on the back substrate 14 for isolating two neighboring address electrodes 20. The fluorescent layer 26 are coated above the address electrode 20 and the sidewalls of each rib for producing red, green or blue light.
Generally speaking, the sustaining electrode 16 is transparent and composed of indium tin oxide (ITO). The transparent electrode is able to penetrate visible light but has a large resistance. The auxiliary electrode 18 is opaque and composed of Cr/Cu/Cr metal layers. The opaque electrode has a poor transparency and good conductivity. Thus, the auxiliary electrode 18 is positioned above the sustaining electrode 16 for increasing the conductivity of the sustaining electrode 16.
Referring to FIG. 2, it is a Paschen curve for showing the relationship between the firing voltage (Vf) of the PDP and the multiplication of the filling gas pressure (P value) with the discharge gap width (D value). When the PD value is equal to a constant C, the firing voltage Vf will reduce to a minimum value. In the present PDP process, the pressure P of the filling gas is increased in order to heighten the brightness under a constant firing voltage as shown in FIG. 3. The filling gas is usually a mixture of Xe and Ne gases. However, as shown in FIG. 2, an increasing P value leads to an increasing Vf value. In order to maintain the Vf value, the D value (discharge gap) must be decreased. The width of the discharge gap 17, the distance between two sustaining electrodes 16, is determined by the photoresist patterned by a mask. However, the accuracy of the patterned photoresist is limited by the resolution of the optical exposure tool and the characteristics of the photoresist materials. Therefore, the pattern with a smaller distance between two sustaining electrode is not easily and exactly transfer to the dry film photoresist for forming a smaller discharge gap 17. Thereby, the large discharge gap will limit the quality of the PDP 10. In addition, a smaller discharge gap can be formed by the high resolution liquid photoresist, but the material cost will be increased. Moreover, the high standard clean room is needed when using the liquid photoresist, and the fabricating cost of the PDP is also increased.
An objective of the present invention is to provide an electrode structure of a plasma display panel with a reduced discharge gap.
The present invention provides an electrode structure of a plasma display panel (PDP). The electrode structure is formed on a front substrate of the PDP. The electrode structure includes a first and a second sustaining electrode, and a first gap is defined between the first and the second sustaining electrode. The electrode structure further includes an auxiliary electrode electrically connected to the first sustaining electrode. The first sustaining electrode has a first side approaching to the second sustaining electrode and a second side far away from the second sustaining electrode.
In addition, the first auxiliary electrode has a first part and a second part, the first part is formed in the first gap, and the second part is formed above the first sustaining electrode and adjacent to the first side of the first sustaining electrode. A second gap exists between the first part of the first auxiliary electrode and the second sustaining electrode, and the width of the second gap is smaller than that of the first gap. The first auxiliary electrode further includes a third part adjacent to the second side of the first sustaining electrode. The third part of the first auxiliary electrode is formed on the surface of the front substrate or on the first sustaining electrode.
The PDP also includes a back substrate parallel to the front substrate, and a plurality of ribs formed on the back substrate and parallel to each other. The ribs are perpendicular to the axial direction of the first auxiliary electrode. The first auxiliary electrode further includes a fourth part parallel to the ribs. The second sustaining electrode includes a third side distal from the first sustaining electrode. The electrode structure also includes a second auxiliary electrode adjacent to the third side of the second sustaining electrode.
A first lithographic process patterns the first and the second sustaining electrodes, and a second lithographic process patterns the first auxiliary electrode. In the present invention, the misalignment of the auxiliary electrode and the sustaining electrode is obtained from twice lithographic processes for forming a smaller discharge gap. As a result, the discharge gap will not be limited by the resolution of the optical exposure tools and photoresist materials in the present invention. Therefore, the discharge gap is reduced and the image quality of the PDP can be improved.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.